So you're thinking of putting in a cement pond? We're actually talking about
ponds for lily pads, fish, turtles and frogs rather than swimming pools.

Some Finished Ponds and Ideas

The 4 major types of ponds are cement, polymer sheet liner, rigid shell, and
clay lined. They all have different strengths and weaknesses. The "best" type of
pond for you may not be the best for someone else.